The invention relates to the performance of hot-press welding of components in particular made of thin material, individually or uniformly on a plurality of surfaces, in course of which coherent bond between the components is achieved by means of a deformable auxiliary material causing mechanical material forming on the surfaces to be connected of two or more components, as well as by the aid of the deforming effect affecting said structural parts.
The process can be expediently used for producing a metallic bond between the components of heat-exchangers of different destination, geometry and material, while the bond is formed from the own material of the components.
Processes are known in course of which the assembled parts--after having performed preparatory works on the surface--dipped into a molten metal bath in order to achieve a metallic bond and a uniform metal coat on the surface, while the coating metal provides a metallic bond between the structural parts. These metal baths consist of heavy metals of low melting point and of their alloys. These are expensive and application is energy-consumptive (e.g. Sn, Sn+Pb, Zn baths).
With other solutions the components to be assembled are coated in advance--partly or entirely--with said heavy metals or their alloys; thereafter the assembled jointless components are covered with a fluxing agent and by heating in a furnace or with a gas-flame they are heated to the melting temperature of the coating metal, as a consequence the metal coating on the surface is melted. Due to inaccuracies of assembly this solution is not at all reliable, in addition, requirement of heavy metals is too high. Such solutions are specified in the Hungarian Patents HU-PS No. 154 673, HU-PS No. 157 652 and HU-PS No. 157 652 (FIGS. 11, 12 and 15.)
Processes are also known in course of which the parts are bound by electric arc welding, shielded arc welding, electric spot welding, ultrasonic welding, i.e. flame-or plasma welding. These processes require a lot of appliances, the productivity is low and due to known difficulties of welding and soldering they are unsuitable for the use with light metals. Such a solutions is to be found in the patent GB-PS No. 1 245 580.
With other processes said diffuculties are eleminated so, that the components are glued with different synthetic materials. However, these are not sufficiently stable and surface preparation is most complicated. Structure of gluing material is different from that of the metal, accordingly it cannot be used for conducting either heat or electricity. They are suitable for processes with a long holding time, as under the heat effect the adhesive becomes decomposed, the stress resulting from different dilatations fatigues the adhesive etc. This solution is partly described in the Hungarian Patent Application No. 2415/80.
Processes are also known in course of which the structural parts are fixed to the connected components by using electric spot welding or ultrasonic welding simultaneously with production. Although--compared to the previously described similar solutions--these represent a progress in respect to productivity, the technological disadvantage cannot be eliminated. Such a solution is specified in the Hungarian Patent HU-PS No. 175 919.
Solutions are known, with which at the heat-exchangers there is only a metallic mechanic connection between the structural element carrying the cooling medium and the heat radiating ribs. As there is no coherent contact, a heat-bridge is formed between the contacting surfaces, accordingly, their heat transmission does not comply with requirements. As a consequence of the different dilatation of the structural elements and shocks arising during operation the contacts may be drifted apart and their thermal output deteriorates. Such a solution is described in the Patent Application No. AO-308.
It has been also proposed that structural parts should be bound by hot-press welding from own material, simultaneously with the production of the components, however, application of said solutions are restricted by successfully with structures made of thin materials, as percentage of material formation needed for hot-press welding (30%) requires an utmost high pressure force or a very high operational temperature in case of thin materials. These two technological conditions are disadvantageously influencing material structure, strength and density of teh unit to be produced.
All the processes proposed mean considerable loading of the producing means in respect to strength and heat, as a consequence, the dimensions of said components do not enable to form dense and high ribs for heat--exchangers, although both geometric requirements form the basis of modern construction and production of heat--and air technical equipments.
In general it can be stated that known solutions have always required thicker materials for material formation, as it had been motivated by the physical properties of the structural material. As a consequence, equipments have been produced with far more material, at higher costs and with an excess-weight, than required by the material characteristics, as if a suitable production technology had been applied.
High loads in respect to strength and thermal load involved with known processes did not enable production of compact heat-exchangers so, that bonds could be formed of the own material of the components, only heat-exchangers with symetrically arranged elements with equal countersupport could be produced.
Such solutions are proposed e.g. in the British Patent GB-PS No. 1 273 141 and in the Hungarian Patent HU-PS No. 175 919.
Compared to prior arts, the present invention represents a progressive process based on new recognitions, eliminating deficiencies of known solutions and yielding increased reliability, as
it guarantees higher productivity, PA1 the bound formed by the process according to the invention is more stable (higher strength can be achieved) and useful life is also longer, PA1 from the point of view of heat flux a more advantageous coherent bound can be obtained, PA1 the bound thus formed resists well to extreme loads, heat and vibration. PA1 with mechanical bonds, with Al/Al structural materials PA1 with soldered Cu/Cu structural material heat resistance amounts to 0,025 KW/m.sup.2 C.degree.; PA1 using aluminium deformable auxiliary material heat resistance of the coherent bound amounts to 0,01 KW/m.sup.2 C.degree..
The invention is based on the following recognitions: Two thin sheets (0,1 to 0,3 mm) can be welded by hotpressing welding in such a manner that onto the defined place of connection an auxiliary material is placed, the thickness of which surpasses by an order of magnitude the thickness of the sheet--e.g. .phi.--and after having heated the components to the temperature of hot-press welding, the two sheets facing each other are pressed with the force F, as a consequence, the auxiliary material will be deformed perpendicularly to the influence line of the force F, while the two sheets are welded on the deformed surface.
With light metals performance of hot-press welding is prevented by the elastic oxyde layer continuously and repeatedly formed on the surface. In a material with a thin cross-section it is most difficult to produce such a deformation which could tear apart the oxyde layer. The novelty of our invention lies in that the deformable auxiliary material adheres to the surfacial part to be welded and due to its advanced deformation it carries the surfacial oxyde layer with itself, as a consequence contact on a surface clean to metal and thus a metallurgic bound can be obtained.
One of the benefits of performing hot-press welding lies in the high-grade material formation, the magnitude of which amounts to about 30 to 50% of the cross-section. The invention is based on the recognition, in so far as, the deformable auxiliary material having been inserted between the surfaces to be welded is pressed into the surface of the materials to be welded under the influence of the force F, auxiliary material is further deformed by the force F, while the auxiliary material is flattened and the sliding material particles carry the crystallites of the surfaces to be welded with themselves, the particles of the deformed material are built-in into the micro-parts having been formed in the crystal lattice of the displaced material, as a consequence, coherent bond is established.
Formation of heat-press weldings depends on temperature, time and compressive strength. If time and temperature are given parameters, formation of the bond will be influenced by the specific compressive force. The invention lies in that unit compressive force becomes a deforming, specifically high and active compressive force due to the fact that the effect is to be considered only in respect to the cross-section of the auxiliary material to be deformed, representing only the fracture of the force, as if the sheet-surfaces to be welded had to be pressed.
The invention is also based on the recognition, in so far as the deformable auxiliary material is formed as a heating unit with electric resistance, in addition to eigenheating radiated heat pre-heats also the surfaces to be welded lying in the environment. When performing hot-press welding, the hottest deformable auxiliary material results in a considerable deformation even, if the compressive force F is less, while the particles in the crystal lattice of the surfaces to be welded become more activated.
A further characteristic of the invention lies in that when used with light metals, electric resistance of the light metal increases with rising temperature, as a consequence, at a given electric output deformable auxiliary material is heating itself.
We have also recognized that in course of prefabrication, at least on one of the surfacial parts to be welded a deforming auxiliary cross-section can be formed. This auxiliary cross-section becomes deformed in course of hot-press welding and a coherent connection is established with the counter-part component.
With pressure-proof vessels stable solid and homogeneous bonds can be formed by using the process according to the invention, resulting in a considerable technological plus-effect in case of light metals.
It is characteristic for the invention that by using the process proposed components with different material thicknesses can be interconnected, so e.g. in course of the production of heat-exchangers ribs or lamellae made of thin sheet material can be welded to media conducting pipes with thicker walls, well tolerating pressure and corrosion.
A further advantageous characteristic of the invention lies in that profiles having a thinner wall can be also used for forwarding the media, as by using the process according to the invention, in course of hot-press welding, the deformed auxiliary material is welded into the thin wall of the profile, thus reinforcing and not weakening it.
According to measurings heat resistances are, as follows:
heat resistance amounts to 0,05 kW/m.sup.2 C.degree.;
Furtheron we recognized that heat transfer ability of bounds having been formed by hot-press welding and using deformable auxiliary materials arranged in predetermined distances surpasses heat transfer capacity of known binding methods. In such a manner heat exchangers with a high efficiency can be produced.
A further recognition lies in that when using the hot-press welding process and the deformable auxiliary material neither fluxing agent nor covering material is needed. The bounds formed of eigenmaterial by hot-press welding yield equipments with a long useful life, well resisting to corrosion without any aftertreatment.
We found that bonds having been formed of the same material by using deformable auxiliary material have the same strength, as the basic material, they are well resistant to vibration, repeated thermal loads and they are insensitive to fatigue.
The invention will be described in detail by means of the drawings enclosed. Taking into consideration that the process according to the invention is mainly applicable in heat-exchanger production, the examples are taken from this field of application.